This application is related to co-pending U.S. patent application Ser. No. 09/573,805, filed May 18, 2000.
1. Field of the Invention
This invention relates to color inkjet recording films, and, more particularly, to water-resistant color-receptive films coated with lightly crosslinked copolymers of vinyl pyrrolidone (VP) and dimethylaminopropyl methacrylamide (DMAPMA).
2. Description of the Prior Art
The advent of color inkjet printing has been instrumental in fueling the print-on-demand revolution and has also created a number of challenges. Often, the surface of the desired media does not possess the necessary properties for accepting the ink-jet ink. This results in long dry times and/or a poor ink-jet image. It has long been recognized that a surface treatment or media coating plays a critical role in the final print quality. Numerous media coatings are known in the art. They may contain any number of components and often consist of more than one layer. These ink-receptive coatings generally contain at least one hydrophilic polymer; often poly(vinylpyrrolidone) (PVP). PVP brings many benefits to properly formulated media coatings including rapid ink dry time, excellent print quality, highly resolved circular dots, and high, uniform optical density. Furthermore, copolymers of vinylpyrrolidone (VP) along with other suitable comonomers, such as dimethylaminoethyl methacrylamide (DMAPMA), acrylic acid, or vinyl acetate, have been used separately or in conjunction with PVP, to further optimize performance. However, it is desired also to provide long-term, excellent water-resistant qualities for such films.
What is described herein is a process for preparing a lightly-crosslinked copolymer of (a) vinyl pyrrolidone (VP) and (b) dimethylaminopropyl methacrylamide (DMAPMA) under more reproducible conditions. Suitably the weight ratio of (a):(b) is 50-90:50-5, preferably 80:20. The copolymer has a Brookfield viscosity of 5,000 to 45,000 cps; preferably 10,000 to 30,000 cps, and a haze of  less than 100 NTU; it includes about 0.1 to 0.5 wt. %, preferably 0.2 to 0.4 wt. %, of a cross-linking agent based upon the total weight of monomers in the copolymer.
Preferably the crosslinking agent is pentaerythritol triallyl ether (PETE), and the polymerization initiator is an azo-type initiator.
The ink-receptive film of the invention is capable of being printed from a color inkjet printer to form superior water-resistant color images thereon.